Such mechanisms have commonly employed a pair of meshing gears of involute tooth form that generally rely upon being tensioned laterally by a spring to improve their grip upon the fabric ribbon and thus ensure the transportation of the ribbon across the printhead. But metal and/or plastic spring devices and the structure or housing to contain them are relatively complex and expensive to manufacture and it is time-consuming and expensive to marshal all the parts for assembly prior to the insertion of the ribbon.
The use of springs can impose a substantial element of stress upon the structure of a cassette which must be compensated for, with friction at the journals putting a substantial torque loading upon the printing mechanism that ultimately draws the ribbon across the face of the printhead and returns it into the chamber. This friction at the gear journals also inhibits high speed loading as heat is generated causing excessive wear at the journals.
It has also been proposed to use a single gear wheel of simple serrated form cooperating with a spring plate, but this arrangement also imposes torque upon the cassette drive.